Color layer composition for chromatic device and method of producing chromatic device by using same

ABSTRACT

A coloring layer composition for a chromatic device of the present invention contains an oxide such as tungsten oxide or niobium oxide and so on as a solute, water and an organic solvent such as propanol. In the step of forming a reduction coloring layer, a film is formed by using a peroxotungstic acid solution containing 100 parts by weight of WO 3 .aNb 2  O 5 .bH 2  O 2 .cH 2  O (wherein a, b and c are each a positive number) as a solute, 20 to 120 parts by weight of water and 80 to 800 parts by weight of n-propanol as an organic solvent. At this time, a dip coating method is used, and the vertical pulling-up speed is less than 15 cm/min. The present invention can effectively prevent unevenness and separation of the reduction coloring layer.

This application is a division of application Ser. No. 08,649,066 filedon May 16,1996 now U.S. Pat. No. 5,851,439, which is a continuation ofapplication Ser. No. 08/295,241 filed on Aug. 24, 1994 (now abandoned).

BACKGROUND OF THE INVENTION

The present invention relates to a coloring layer composition for achromatic device, and a method of producing a chromatic device by usingthe composition. The composition can be used in, for example, a coloringlayer formation process for forming a reduction coloring layer of anelectrochromatic (EC) device.

A known chromatic device, e.g., EC device, comprises a first transparentsubstrate 1, a first electrode layer 2, a reduction coloring layer 3, anelectrolyte layer 4, an oxidation coloring layer 5, a second transparentelectrode layer 6 and a second transparent substrate 7, which aresuccessively laminated as shown in FIG. 1. In this EC device, when acurrent higher than the determined threshold value is applied betweenthe first electrode layer 2 and the second electrode layer 6, oxidationand reduction reactions take place in the vicinities of the interfacesbetween the first electrode layer 2 and the reduction coloring layer 3and between the second electrode layer 6 and the oxidation coloringlayer 5 to obtain a reversible coloration-bleaching change.

In the EC device, tungsten oxide (WO₃) can be used for the reductioncoloring layer 3. Known methods of forming the reduction coloring layer3 comprising WO₃ include general dry methods such as a sputtering methodand an evaporation method, a spin coating method for forming a film byusing a peroxotungstic acid solution as disclosed in "Applied Physics"No. 61, Vol. 3 (1992) (pp. 226-269), and a dip coating method forforming a film by using the some peroxotungstic acid solution. Otherknown methods of forming the reduction coloring layer in the EC deviceinclude methods using a solution containing an organic compound of W, asdisclosed in Japanese Patent Laid-Open Nos. 56-38379, 61-36292,61-123691 and 62-112132.

However, if a dry method such as a sputtering or evaporation method isperformed, a large vacuum apparatus is required for obtaining alarge-area EC device, thereby increasing the production cost.Particularly, if the sputtering method is executed, since thetemperature of the substrate used is increased, a glass substrate can beused, but a resin substrate cannot, thereby hindering the light weightproperties of the EC device.

Even if the spin coating method is performed, the coloring layer can beobtained without an increase in the production costs only when asubstrate of about 30 cm square is rotated, and thus larger EC devicecannot be produced at low cost.

It thus seems practically effective when producing a large EC device atlow cost to perform the dip coating method. Wet methods such as printingmethods, spray methods, spin coating methods and so on other than thedip coating method also seem to be practically effective.

However, the results of the tests performed by the inventors showed thatthe wet dip coating method causes wave-like flows in the film afterpulling up the substrate, and thus causes unevenness in the reductioncoloring layer formed by drying the film as is. Particularly, if theperoxotungstic acid solution is used in the dip coating method, bubblesoccur in the film due to the generation of oxygen caused by thedecomposition reaction of the hydrogen peroxide contained in thesolution, and the release of the oxygen dissolved therein during thedipping and pulling-up of the substrate. If the film is dried as is,unevenness occurs in the reduction coloring layer formed. Since theunevenness in the reduction coloring layer can be visually confirmed,and as it causes unevennes in the transmittance of the EC device duringcoloring, quality problems arise.

In addition, although a uniform film can be formed immediately afterpulling up the substrate, heat treatment of the film in post-processingcauses cracks in the reduction coloring layer and in turn separation ofthe layer. The cracks and separation bring about contact between theelectrolyte layer and the first electrode layer of the EC device,thereby causing quality problems due to deterioration or dissolution ofthe first electrode layer. If a large EC device is produced, unevennessin or separation of the reduction coloring layer is particularlyconspicuous, and utility thus significantly deteriorates. A wet methodusing a solution containing an organic compound of tungsten has thedrawback that preparation of the organic compound is troublesome.

The above drawbacks apply to not only the EC device but also otherchromatic devices such as thermochromatic devices, photochromaticdevices and so on which have a coloring layer comprising an oxide of atleast one of W, Nb, Mo and V.

The present invention has been achieved in consideration of the aboveactual conditions, and an object of the present invention is to permitreliable production of a large chromatic device at low cost.

Another object of the present invention is to provide a novel coloringlayer composition used for forming a reduction coloring layer of achromatic device.

A further object of the present invention is to provide a high-qualitychromatic device on which a coloring layer is formed by using the abovecomposition under specified conditions so as to prevent unevennes in andseparation of the coloring layer.

As a result of intensive studies performed by the inventors for solvingthe above problems, it was found that the mixing of an organic solventwith a coloring layer forming composition is effective for decreasingthe surface energy of the film formed and effective in preventingunevenness in and separation of the film. It was also found that theorganic solvent can prevent oxygen from generating due to thedecomposition of hydrogen peroxide, and in prevent the dissolved oxygenfrom being released. The organic solvent is required to havecompatibility with water because a solute comprising an oxide of atleast one of W, Nb, Mo and V is dissolved in water, and to be evaporatedby heat treatment of the film. This resulted in the achievement of thepresent invention. It was further found that a film of a coloring layerwithout unevenness or separation can be formed by employing a dipcoating method and vertically pulling up the treated substance at a lowspeed.

SUMMARY OF THE INVENTION

The present invention provides a coloring layer composition for achromatic device comprising a solute comprising an oxide of at least oneof W, Nb, Mo and V, water for dispersing and holding the solute, and anorganic solvent compatible with water.

The present invention also provides a coloring layer composition for achromatic device comprising as a solute a tungsten oxide-containingcompound represented by the formula WO₃.aNb₂ O₅.bH₂ O₂.cH₂ O (wherein a,b and c are each zero or a positive number).

The present invention further provides a coloring layer composition fora chromatic device comprising a peroxotungstic acid solution containingas a solute 100 parts by weight of WO₃.aNb₂ O₅.bH₂ O₂.cH₂ O (wherein a,b and c are each a positive number), 20 to 120 parts by weight of waterand 80 to 800 parts by weight of propanol as an organic solvent.

The present invention further provides a method of producing a chromaticdevice having a first transparent substrate, a first transparentelectrode layer, a reduction coloring layer, an electrolyte layer, anoxidation coloring layer, a second transparent electrode layer and asecond transparent substrate, which are successively laminated, themethod comprising the step of forming the reduction coloring layer onthe first transparent electrode layer. The reduction coloring layerforming step employs a dip coating method for forming a film on thefirst transparent electrode layer by using the above coloring layercomposition, the vertical pulling-up speed being less than 15 cm/min.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating an EC device; and

FIGS. 2 to 9 are graphs each illustrating the relation between thepulling-up speed and the thickness of a film when it is formed on afirst electrode layer by using a coloring layer composition (8 typeshaving different compositions) of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A coloring layer composition of the present invention contains a soluteconsisting of an oxide of at least one of W, Nb, Mo and V, water fordispersing and holding the solute and an organic solvent compatible withwater. The organic solvent decreases the surface energy of the filmformed and thus effectively prevents unevenness and separation of thecoloring layer. The organic solvent compatible with water does notinterfere with dissolution of the solute in water and is evaporated byheat treatment of the film.

Examples of the solute include tungsten oxide (for example, WO₃),niobium oxide (for example, Nb₂ O₅), molybdenum oxide (for example, Mo₂O₅), vanadium oxide (for example, V₂ O₅) and a mixture or complex ofthese oxides. Preferred examples of the solute are tungstenoxide-containing compounds represented by the following formula:

WO₃.aNb₂ O₅.bH₂ O₂.cH₂ O (wherein a, b and c are each zero or a positivenumber)

Of these compounds, compounds in which a, b and c are each a positivenumber are more preferred. The compounds are heteropolyacids obtained bytreating powders of tungsten and niobium metals or metal compounds withhydrogen peroxide. The compound is referred to as "peroxotungstic acid"hereinafter. Although a solution of the peroxotungstic acid easilyproduces bubbles due to the hydrogen peroxide contained therein, theorganic solvent compatible with water can prevent oxygen from generatingdue to the decomposition of hydrogen peroxide, and can prevent thedissolved oxygen from being released.

Furthermore, compounds represented by the formulae: WO₃.aMoO₂.bH₂ O₂.cH₂O; MoO₂.aNb₂ O₅.bH₂ O₂.cH₂ O; WO₃.aNb₂ O₅.bMoO₂.cH₂ O₂.dH₂ O; and V₂O₅.aH₂ O₂.bH₂ O; (wherein a, b and c and d each zero or a positivenumber), may be used as a solute.

In the composition of the present invention, water and an organicsolvent are used as solvents. Examples of suitable organic solventswhich are soluble or compatible with water and capable of inhibitingdecomposition of hydrogen peroxide and/or retarding the release ofdissolved oxygen include: alcohols, preferably alkyl alcohols, such asthe lower (C₁ -C₅); oxygenated derivatives of alcohols such as alkoxyalkanols, e.g., 2-ethoxyethanol; dialkyl amides such as dialkylalkamides, e.g., dimethyl formamide.

The amount of the solute present in the composition of the presentinvention is 50% by weight, preferably 20 to 30% by weight, of the totalamount of the composition.

The amount of the organic solvent used is 80 parts by weight, preferably80 to 800 parts by weight, relative to 100 parts by weight of thesolute.

A preferred coloring layer composition according to the presentinvention comprises 100 parts by weight of WO₃.aNb₂ O₅.bH₂ O₂.cH₂ O(wherein a, b and c are each zero or a positive number) as a solute, notmore than 120 parts by weight, preferably 20 to 120 parts by weight, ofwater, and at least 80 parts by weight, preferably 80 to 800 parts byweights of propanol as the organic solvent. The use of the compositioncan effectively prevent unevenness in and separation of the coloringlayer.

The method of producing an EC device by using the coloring layercomposition of the present invention employs the dip coating method in aportion of the reduction coloring layer forming step. Namely, a film isformed on a first transparent electrode layer by using a peroxotungsticacid solution. The solvent is removed from the film by heat treatment toform a reduction coloring layer comprising WO₃.aNb₂ O₅.bH₂ O₂.cH₂ O(wherein a, b and c are each zero or a positive number) as a solute.

As a result of tests performed by the inventors, it became clear thatunevenness occurs in the reduction coloring layer due to a wave-likeflow of the film after vertically pulling the substrate up from theperoxotungstic acid solution under the conditions of low concentrationof the solution (also low viscosity) and a high pulling-up speed, whichcauses adhesion of a large amount of solution.

Under the conditions of high concentration and high pulling-up speed,wihich cause the formation of a thick film, cracks occur in thereduction coloring layer. It seems that when the film thickness isincreased, cracks can occur due to an increase in the internal stress ofthe film during heat treatment. This is liable to produce separation ofthe film.

It is thus effective for preventing the generation of unevenness andseparation that the solute concentration of the coloring layer formingcomposition be less than 50% by weight, preferably 20 to 30% by weight,and the vertical pulling-up speed less than 15 cm/min, preferably lessthan 10 cm/min.

EXAMPLES

Although the present invention is described in detail below withreference to an example and test examples, the present invention is notlimited to these examples.

(Preparation of coloring layer composition)

The EC device shown in FIG. 1 as an example of chromic devices wasproduced by using an example of a reduction coloring layer composition.The EC device is characterized by the reduction coloring layercomposition, and thus has the same appearance as that of a conventionaldevice.

First, the reduction coloring layer composition (peroxotungstic acidsolution) was obtained. That is, 0.18 mole of tungsten powder and 0.015mole of niobium carbide powder were dissolved in 200 ml of 15% hydrogenperoxide aqueous solution. The resultant solution was then dried under areduced pressure to synthesize a powder of WO₃.0.041 Nb₂ O₆ O.6H₃ O₃.3H₂O (referred to as "IPA powder" hereinafter). The IPA powder wasdissolved in pure water to obtain a solution containing the IPA powder.The thus-formed solution contained 100 parts by weight of IPA powder asa solute and 24 parts by weight of water.

The solution was diluted with n-propanol to obtain a peroxotungstic acidsolution containing the IPA powder. The resultant peroxotungstic acidsolution contained 100 parts by weight of IPA powder as a solute, 24parts by weight of water and 230 parts by weight of n-propanol.

(Production of EC device)

The EC device was produced by the following method: A PET transparentresin film (5 cm×5 cm) was used as first and second transparentsubstrates 1 and 7. ITO (indium tin oxide (In₂ O₃.SnO₂)) was depositedon the surfaces of the first and second transparent substrates 1 and 7to form first and second electrode layers 2 and 6, respectively,comprising ITO. In this way, a multiple first ITO film comprising thefirst transparent substrate and the first electrode layer 2, and amultiple second ITO film comprising the second transparent substrate 7and the second electrode layer 6 were obtained.

The first ITO film was then dipped in the peroxotungstic acid solution,and then vertically pulled up at a pulling-up speed of 0 to 10 cm/mn. Inthis way, a film was formed by the dip coating method, In this case, nowave-like flows occurred in the film after pulling it up.

The first ITO film on which the film was formed was then subjected toheat treatment at 120° C. for 1 hour for removing moisture from the filmto form a reduction coloring layer 3 comprising WO₃.0.041 Nb₂ O₅ on thefirst electrode layer 2. No unevenness, cracking or separation occurredin the reduction coloring layer 3.

The first ITO film was dipped in a LiCF₃ SO₃.propylene carbonate (PC)solution to inject Li ion in the WO₃.0.041 Nb₃ O₅.

Meanwhile, a Prussian blue (Fe²⁺ [Fe³⁺ (CN)₆ ³⁻ ]) was deposited on thesecond electrode layer 6 of the second ITO film which was washed withalkali, by an electrolytic synthetic method to form an oxidationcoloring layer 5 comprising the Prussian blue film.

An electrolyte solution was prepared by dissolving a supporting salt(LiCF₃ SO₄) and a photopolymerization initiator(2,2-dimethoxy-2-phenylacetophenone) in polyethylene oxide, and coatedon the oxidation coloring layer 5 of the second ITO film.

The reduction coloring layer 3 of the first ITO film and the electrolytesolution on the second ITO film were bonded, and then irradiated withultraviolet rays (UV) for curing the electrolyte solution to form anelectrolyte layer 4 from the electrolyte solution.

It was confirmed that the thus-obtained EC device produced excellentreversible coloration-bleaching changes.

Accordingly, the reduction coloring layer composition (peroxotungsticacid solution) of the present invention of the example can effectivelyprevent the occurrence of unevenness and separation in the reductioncoloring layer formed by the dip coating method, thereby making itpossible to reliably produce a large EC device at low cost.

(Test 1)

An optimum composition range of the reduction coloring layer composition(peroxotungstic acid solution) was determined.

First, an IPA powder was synthesized by the same method as that employedin the Example. The IPA powder was then dissolved in pure water toobtain each of the solutions A to G having the compositions in parts byweight shown in TABLE 1.

                  TABLE 1                                                         ______________________________________                                        Solution No.                                                                              A      B      C    D    E    F    G                               ______________________________________                                        IPA (parts by weight)                                                                     100    100    100  100  100  100  100                             Water (parts by                                                                           20     24     40   60   80   100  120                             weight)                                                                       ______________________________________                                    

Solution A was diluted with the amounts of n-propanol shown in TABLE 2to obtain the peroxotungstic acid solutions No. 1 to No. 10. TABLE 2also shows the relation between the pulling-up speed (cm/min) and thestate of the reduction coloring layer when each of the peroxotungsticacid solutions No. 1 to No. 10 was used in the dip coating method. Theother conditions were the same as those employed in the Example (thesame applies hereinafter). In TABLE 2, the mark ∘ indicates that anexcellent reduction coloring layer was formed, Δ indicates that cissingoccured in the reduction coloring layer, ▴ indicates that unevennessoccured in the reduction coloring layer, and x indicates that separationoccured in the reduction coloring layer (the same applies hereinafter).FIG. 2 shows the relation between the pulling-up speed (cm/min) and thethickness of the reduction coloring layer (μm) when some of theperoxotungatic acid solutions were used in the dip coating method.

                                      TABLE 2                                     __________________________________________________________________________    Solution No.                                                                            1 2 3  4  5  6  7  8  9  10                                         __________________________________________________________________________    Amount of n-propanol                                                                    40                                                                              80                                                                              100                                                                              130                                                                              160                                                                              230                                                                              280                                                                              400                                                                              500                                                                              800                                        (parts by weight)                                                             Pulling-up rate                                                               1 cm/min. X ∘                                                                   ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                              3 cm/min. X X ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                              6 cm/min. X X ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                              __________________________________________________________________________

Solution B was diluted with the amounts of n-propanol shown in TABLE 3to obtain the peroxotungstic acid solutions No. 11 to No. 17. TABLE 3also shows the relation between the pulling-up speed (cm/min) and thestate of the reduction coloring layer when each of the peroxotungsticacid solutions No. 11 to No. 17 was used in the dip coating method. FIG.3 shows the relation between the pulling-up speed (cm/min) and thethickness of the reduction coloring layer (μm) when some of theperoxotungstic acid solutions were used in the dip coating method.

                  TABLE 3                                                         ______________________________________                                        Solution No. 11    12    13   14   15   16   17                               ______________________________________                                        Amount of n-propanol                                                                       40    80    100  130  160  230  280                              (parts by weight)                                                             Pulling-up rate                                                               1 cm/min.    X     ∘                                                                       ∘                                                                      ∘                                                                      ∘                                                                      ∘                                                                      ∘                    3 cm/min.    X     X     ∘                                                                      ∘                                                                      ∘                                                                      ∘                                                                      ∘                    6 cm/min.    X     X     ∘                                                                      ∘                                                                      ∘                                                                      ∘                                                                      ∘                    ______________________________________                                    

Solution C was diluted with the amounts of n-propenol shown in TABLE 4to obtain the peroxotungstic acid solutions No. 18 to No. 27. TABLE 4also shows the relation between the pulling-up speed (cm/min) and thestate of the reduction coloring layer when each of the peroxotungsticacid solutions No. 18 to No. 27 was used in the dip coating method. FIG.4 shows the relation between the pulling-up speed (cm/min) and thethickness of the reduction coloring layer (μm) when some of theperoxotungstic acid solutions were used in the dip coating method.

                                      TABLE 4                                     __________________________________________________________________________    Solution No.                                                                            18 19                                                                              20 21 22 23 24 25 26 27                                        __________________________________________________________________________    Amount of n-propanol                                                                    40 80                                                                              100                                                                              130                                                                              160                                                                              230                                                                              280                                                                              400                                                                              500                                                                              800                                       (parts by weight)                                                             Pulling-up rate                                                               1 cm/min. ∘                                                                    ∘                                                                   ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                             3 cm/min. Δ▴                                                          ∘                                                                   ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                             6 cm/min. Δ▴                                                          ▴                                                                ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                             __________________________________________________________________________

Solution D was diluted with the amounts of n-propanol shown in TABLE 5to obtain the peroxotungstic acid solutions No. 28 to No. 37. TABLE 5also shows the relation between the pulling-up speed (cm/min) and thestate of the reduction coloring layer when each of the peroxotungsticacid solutions No. 28 to No. 37 was used in the dip coating method. FIG.5 shows the relation between the pulling-up speed (cm/min) and thethickness of the reduction coloring layer (μm) when some of theperoxotungstic acid solutions were used in the dip coating method.

                                      TABLE 5                                     __________________________________________________________________________    Solution No.                                                                            28 29 30 31 32 33 34 35 36 37                                       __________________________________________________________________________    Amount of n-propanol                                                                    40 80 100                                                                              130                                                                              160                                                                              230                                                                              280                                                                              400                                                                              500                                                                              800                                      (parts by weight)                                                             Pulling-up rate                                                               1 cm/min. Δ▴                                                          ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            3 cm/min. Δ▴                                                          ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            6 cm/min. Δ▴                                                          Δ▴                                                          ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            __________________________________________________________________________

Solution E was diluted with the amounts of n-propanol shown in TABLE 6to obtain the peroxotungstic acid solutions No. 38 to No. 47. TABLE 6also shows the relation between the pulling-up speed (cm/min) and thestate of the reduction coloring layer when each of the peroxotungsticacid solutions No. 38 to No. 47 was used in the dip coating method. FIG.6 shows the relation between the pulling-up speed (cm/min) and thethickness of the reduction coloring layer (μm) when some of theperoxotungstic acid solutions were used in the dip coating method.

                                      TABLE 6                                     __________________________________________________________________________    Solution No.                                                                            38 39 40 41 42 43 44 45 46 47k                                      __________________________________________________________________________    Amount of n-propanol                                                                    40 80 100                                                                              130                                                                              160                                                                              230                                                                              280                                                                              400                                                                              500                                                                              800                                      (parts by weight)                                                             Pulling-up rate                                                               1 cm/min. Δ▴                                                          Δ▴                                                          ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            3 cm/min. Δ▴                                                          Δ▴                                                          ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            6 cm/min. Δ▴                                                          Δ▴                                                          Δ▴                                                          ▴                                                                 ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            __________________________________________________________________________

Solution F was diluted with the amounts of n-propanol shown in TABLE 7to obtain the peroxotungstic acid solutions 48 to 57. TABLE 7 also showsthe relation between the pulling-up speed (cm/min) and the state of thereduction coloring layer when each of the peroxotungstic acid solutionsNo. 48 to No. 57 was used in the dip coating method. FIG. 7 shows therelation between the pulling-up speed (cm/min) and the thickness of thereduction coloring layer (μm) when some of the peroxotungstic acidsolutions were used in the dip coating method.

                                      TABLE 7                                     __________________________________________________________________________    Solution No.                                                                            48 49 50 51 52 53 54 55 56 57                                       __________________________________________________________________________    Amount of n-propanol                                                                    40 80 100                                                                              130                                                                              160                                                                              230                                                                              280                                                                              400                                                                              500                                                                              800                                      (parts by weight)                                                             Pulling-up rate                                                               1 cm/min. Δ▴                                                          Δ▴                                                          ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            3 cm/min. Δ▴                                                          Δ▴                                                          Δ▴                                                          ▴                                                                 ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            6 cm/min. Δ▴                                                          Δ▴                                                          Δ▴                                                          ▴                                                                 ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            __________________________________________________________________________

Solution G was diluted with the amounts of n-propanol shown in TABLE 8to obtain the peroxotungstic acid solutions No.58 to No. 67. TABLE 8also shows the relation between the pulling-up speed (cm/min) and thestate of the reduction coloring layer when each of the peroxotungsticacid solutions No. 58 to No. 67 was used in the dip coating method. FIG.8 shows the relation between the pulling-up speed (cm/min) and thethickness of the reduction coloring layer (μm) when some of theperoxotungstic acid solutions were used in the dip coating method.

                                      TABLE 8                                     __________________________________________________________________________    Solution No.                                                                            58 59 60 61 62 63 64 65 66 67                                       __________________________________________________________________________    Amount of n-propanol                                                                    40 80 100                                                                              130                                                                              160                                                                              230                                                                              280                                                                              400                                                                              500                                                                              800                                      (parts by weight)                                                             Pulling-up rate                                                               1 cm/min. Δ▴                                                          Δ▴                                                          ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            3 cm/min. Δ▴                                                          Δ▴                                                          Δ▴                                                          ▴                                                                 ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                            6 cm/min. Δ▴                                                          Δ▴                                                          Δ▴                                                          ▴                                                                 ▴                                                                 ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                            __________________________________________________________________________

As seen from TABLES 2 to 8 and FIGS. 2 to 8, a peroxotungstic acidsolution containing 100 parts by weight of IPA powder, not more than 120parts by weight of water and not less than 80 parts by weight ofn-propanol as an organic solvent can effectively prevent unevenness inand separation of the reduction coloring layer. It is also found thatthe peroxotungstic acid solution containing 100 parts by weight of IPApowder, 20 to 120 parts by weight of water, and 80 to 800 parts byweight of n-propanol as an organic solvent can effectively preventunevenness in and separation of the reduction coloring layer.

(Test 2)

Other organic solvents for the reduction coloring layer composition(peroxotungstic acid solution) were investigated.

First, IPA powder was first synthesized by the same method as thatemployed in the Example. The thus-synthesized power was dissolved inpure water to obtain solution B having the composition in parts byweight shown in TABLE 1.

Solution B was diluted with the amounts of 2-ethoxyethanol shown inTABLE 9 to obtain the peroxotungstic acid solutions No. 68 to No. 77.TABLE 9 also shows the relation between the pulling-up speed (cm/min)and the state of the reduction coloring layer when each of theperoxotungstic acid solutions No. 68 to No. 77 was used in the dipcoating method. FIG. 9 shows the relation between the pulling-up speed(cm/min) and the thickness of the reduction coloring layer (μm) whensome of the peroxotungstic acid solutions were used in the dip coatingmethod.

                                      TABLE 9                                     __________________________________________________________________________    Solution No.                                                                              68 69 70 71 72 73 74 75 76 77                                     __________________________________________________________________________    Amount of 2-ethoxyethanol                                                                 40 80 100                                                                              130                                                                              160                                                                              230                                                                              280                                                                              400                                                                              500                                                                              800                                    (parts by weight)                                                             Pulling-up rate                                                               1 cm/min.   Δ▴                                                          ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                          3 cm/min.   Δ▴                                                          ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                          6 cm/min.   Δ▴                                                          Δ▴                                                          ▴                                                                 ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                                                                    ∘                          __________________________________________________________________________

It can be understood from TABLE 9 and FIG. 9 that 2-ethoxyethanol can beused as the organic solvent.

Although dimethylformamide can be used as the organic solvent, theresults of the tests performed by the inventors showed thatdimethylformamide is difficult to use because the composition containingdimethylformamide produces a precipitate of the IPA powder withinseveral hours.

Although the above Example and Tests 1 and 2 employ the wet dip coatingmethod for coating the composition, the composition of the presentinvention can be applied to other wet methods. However, when a wet spincoating method is executed, an EC device can be produced withoutsignificant increase in the production cost only when a substrate ofabout 30 cm square is rotated, and generally difficulties arise inproducing a larger EC device at low cost.

Although the above Example and Tests 1 and 2 each relates to an ECdevice of chromatic devices, the application of the composition of thepresent invention is not limited to the EC device, and the compositioncan be applied to other chromatic devices such as thermochromaticdevices, photochromatic devices and so on, which have a reductioncoloring layer comprising an oxide of at least one of W, Nb, Mo and V.

As described above, the coloring layer composition for a chromaticdevice according to the present invention is constructed as described ineach of the Claims, and thus the composition can effectively prevent theoccurrence of unevenness in and separation of the coloring layerproduced by a wet method such as the dip coating method.

The use of this composition thus improves the utility of the wet methodsuch as the dip coating method, and permits reliable production of alarge chromatic device at low cost.

What is claimed is:
 1. A method of producing a chromatic device having afirst transparent substrate, a first transparent electrode layer, areduction coloring layer, an electrolyte layer, an oxidation coloringlayer, a second transparent electrode layer and a second transparentsubstrate, which are successively laminated, said method comprising areduction coloring layer forming step for forming said reductioncoloring layer on said first transparent electrode layer;wherein saidreduction coloring layer forming step employs a dip coating method forforming a film on said first transparent electrode layer by using acoloring layer composition comprising a solute comprising a metaloxide-containing compound selected from the group consisting of WO₃.aNb₂O₅.bH₂ O₂.cH₂ O, WO₃.aMoO₂.bH₂ O₂.cH₂ O, MoO₂.aNb₂ O₅.bH₂ O₂.cH₂ O,WO₃.aNb₂ O₅.bMoO₂.cH₂ O₂.dH₂ O, and V₂ O₅.aH₂ O₂.bH₂ O (wherein a, b, cand d are each zero or a positive number), water for dispersing andholding said solute, and an organic solvent compatible with water, thevertical pulling-up speed being less than 15 cm/min.
 2. A method ofproducing a chromatic device according to claim 1, wherein saidreduction coloring layer forming step employs a dip coating method forforming a film on said first transparent electrode layer by using saidcoloring layer composition containing 20 to 30% by weight of WO₃.aNb₂O₅.bH₂ O₂.cH₂ O (wherein a, b and c are each zero or a positive number)as said solute, the vertical pulling-up speed being less than 10 cm/min.